Recently, with the demand of high image quality and energy saving in an electrophotographic technique, reduction of a toner particle diameter and low-temperature fixation of a toner are proceeding.
However, it becomes difficult to further reduce a toner particle diameter using a conventional kneading pulverizing method. Therefore, as a production method of a toner capable of reducing the particle diameter, a wet-type production method of a toner attracts attention. As an example of such a wet-type production method, there is an agglomeration method as described in JP-A-60-225170, JP-A-63-282749, JP-A-6-282099, etc. This agglomeration method is a method of obtaining a toner by agglomerating fine particles of toner components such as a binder resin, a colorant and a releasing agent in a medium such as water using an agglomerating agent such as a metal salt by intentionally destroying the dispersed state of the respective fine particles thereby obtaining agglomerated particles, and thereafter fusing the surface of the agglomerated particles by subjecting the agglomerated particles to a heat treatment. This fusion step is sometimes performed simultaneously with the agglomeration step when an agglomeration temperature capable of achieving a target particle diameter is not lower than the glass transition temperature of the binder resin. In this method, toner particles are produced by agglomerating and fusing fine particles on the order of submicrometer, therefore, by using this method, toner particles having a particle diameter of 5 μm or less can be produced, and therefore a high quality image can be provided. Further, when this agglomeration method is used, by changing a condition for fusion, the shape of a toner can be controlled from an irregular shape to a spherical shape. Further, by changing a condition for agglomeration, the dispersion state of a wax, a pigment, a charge control agent and the like in the toner can be controlled at will.
On the other hand, with the advancement of low-temperature fixation of a toner, a polyester resin attracts attention in place of a conventional styrene acrylic resin as the binder resin. The use of a polyester resin can achieve both low-temperature fixability and storability of a developing agent. However, in a conventional agglomeration method, it is difficult to polymerize polyester and pulverize the resulting polymerized polyester into fine particles in water, therefore, the conventional agglomeration method could be applied only to a styrene acrylic resin through emulsion polymerization. On the other hand, as an agglomeration method suitable for a polyester resin, a method in which a polyester resin is melted by heating the resin or using a solvent, the resulting molten resin is mechanically pulverized into fine particles, and then agglomerated is proposed. JP-A-2007-323071 discloses a method of mechanically pulverizing a toner component material into fine particles without using a solvent after the toner component material is melt-kneaded or mixed. When this method is used, a colorant is uniformly dispersed in a binder resin, therefore, this method is extremely superior as a production method of a color toner. Further, because this method is solventless, it is an excellent production method capable of reducing an environmental load.
However, when this agglomeration method suitable for a polyester resin is used, a metal salt is used as an additive for destroying the dispersibility of fine particles. Therefore, when this metal salt remains in the toner, pseudo-crosslinking between molecules is accelerated and the fusibility of a toner is deteriorated. As a result, the low-temperature fixability of a toner is deteriorated.
In order to improve the above disadvantages of a metal salt, a novel agglomeration method without using a metal salt is proposed. JP-A-6-110252 proposes an agglomeration method using a quaternary ammonium salt compound, JP-A-2003-316068 proposes an agglomeration method using a polymeric agglomerating agent, and further, JP-A-6-214418 proposes an agglomeration method using an ionic surfactant with a polarity reverse to that of particles.
However, when a cationic surfactant as disclosed in JP-A-6-110252 and JP-A-6-214418 is used, because only one cationic group is present per molecule, the agglomerating property is very low, and therefore, it is necessary to add the cationic surfactant in a large amount. Due to this, the amount of the cationic surfactant remaining in the toner is increased, and the chargeability of the toner is deteriorated due to the hydrophilic group of the surfactant. Further, when a polymeric agglomerating agent having a molecular weight of 100000 or more as disclosed in JP-A-6-110252 and JP-A-2003-316068 is used, because the molecule is too large, an increase in the viscosity of the system or crosslinking between particles is caused, and coarse particles and unagglomerated particles are liable to be formed, and it is difficult to obtain a uniform particle size distribution.